The cyclic model

The cyclic model was introduced in this paper:
"A cyclic model of the universe"http://arxiv.org/abs/hep-th/0111030
and is a idea of Steinhardt and Turok. (Some might some day recognize the great quantities of ideas that Steinhardt has introduced in the last 30 years).
The model proposes an universe with no beginning, existing since infinite time. We inhabit in a brane, and there's another brane that is a "mirror image" of our brane, and this two branes periodically collide, the Big Bang is produced, then they separate, and turn to collide and so on. Very simple. No metaphysics questions about the beginning.Is postulated that one brane has positive tension and the other negative tension. Now, what this means? I can't make head and tails of what means negative tension.
And, what means that the other brane is a mirror image of our brane? Does it mean that there's another Physicsforums,another new year's day, another Eiffel tower, in the other brane?

Originally posted by meteor The cyclic model was introduced in this paper:
"A cyclic model of the universe"
The model proposes an universe with no beginning, existing since infinite time. We inhabit in a brane, and there's another brane that is a "mirror image" of our brane, and this two branes periodically collide, the Big Bang is produced, then they separate, and turn to collide and so on. Very simple. No metaphysics questions about the beginning.Is postulated that one brane has positive tension and the other negative tension. Now, what this means? I can't make head and tails of what means negative tension.

If there is no beginning, then doesn't that just beg the question as to where the universe came from?

Originally posted by Mike2 If there is no beginning, then doesn't that just beg the question as to where the universe came from?

I consent. It used to be a tradition to disregard these sort of questions as being "meaningless", and without a clear intuition in mind (without referring, as a last resort, to the antropic principle), but with the advent of string theory and loop quantum gravity, the question comes up as a natural inquiry in the theory.

The Cyclic Model merely remediates some shortcomings the original models had many years ago, and by doing so, fits in pretty damn close to the current observed accelerated universe. Suffice to say though, it borrows heavily from a more contemporary, and while we're at it, attractive proposal, "Ekpyrotic Universe" and the various "Pre-big Bang" scenarios before and after it (not to mention the quite recent "Branegas Cosmology" picture).

Finding a "background independent" (non-perturbative) regime of M-Theory (which constitutes the myriad of string theories out there through all sorts of dualities) would go a long way towards preempting the prevailing notion of these nonsensical, orthic questions and firmly rely the results to the rest of the world.

Hopefully, splicing LQG & String Theory in one way or another, may be just what the doctor ordered for solving this perpetual enigma.

p.s
At the end of the day, it all boils down to "elegancy" and the Cyclic proposition, does nothing to mitigate the extremely limited, in essence, and if i may add, mundane collage of the universe it presents us with.

If there is no beginning, then doesn't that just beg the question as to where the universe came from?

The cyclic model says that the two three dimensional branes have been colliding and separating from an infinite past. I like the idea, cause I'm lately having preferences for cosmologies without beginning, my favourite is LQC, but like alexsok said, the cyclic model is a derivation of the ekpyrotic universe, and is really a sound proposal. (If you like scenarios of this kind, read about the "pyrotechnic universe", an idea of Andrei Linde, that is also a derivation of the ekpyrotic universe)
What the cyclic model proposes is that, after the two branes collide, they separate and expand for at least a trillion (1012) of years, then the branes contract, turn to collide, and the cycle begins another time. There's no period of inflation in our brane in the cyclic model, but the dynamics of contraction/expansion are driven by the same scalar field, a kind of quintessence acting like a dark energy driving the expansion and the contraction. But this is practically all my knowledge about the cyclic model, I have to read more about it

Originally posted by meteor What the cyclic model proposes is that, after the two branes collide, they separate and expand for at least a trillion (1012) of years, then the branes contract, turn to collide, and the cycle begins another time.

Let the question begging begin: Then where did the two branes come from?

The branes have existed forever. They have been colliding and separating forever, the problem is that I don't understand very much the mechanism attraction/repulsion between them, seems that exist some interbrane force driven by some kind of potential. Branes existing forever is not more absurd that the idea postulated by standard big Bang (appearance of spacetime at time zero)

Originally posted by Mike2 Let the question begging begin: Then where did the two branes come from?

The gist of your inquiry is basically the same as the naive questioning we grappled with so fiercely, attempting ferociously to find an applicable and reciprocal principle, according to which, our universe is governed, consentaneous with the Big Bang cosmology and etymologizing of it's inevitable origin. No my friends, no such principle sought, would be discovered, if we keep walloping our heads at a stalwart wall!

Despite what some people would say, this is PRECISELY the issue at hand here! Allow me to provide a living example. NASA's latest probe to Mars, Spirit, has lifted the curtain a bit, and cushioned itself of the imprecations from the not too fruitful future, but the clock is ticking, and chances abreast it! It wouldn't surprise me one bit, if the entire mission turns out to be a big chit-chat, and no traces of life whatsoever come floating over the air. The reason is extremely explicable: we might not "operate" according to the right mechanism we should if we're to delineate any life on Mars! We all are unimaginably accustomed to the life conditions on Earth, and thus, function according to common axioms and postulates, familiar to us! Perhaps life on Mars are manuevered by entirely different mechanics, unknown to us, and we all excogorate and persist in keeping our faith at something we do not comprehend at all!

We are "Earth-centric" mate, but can you say that we're ignorant and exceedingly nascient? Sure you can! Delving into this matter is worthwhile, and unless the tentative answers we're provisioned with are copasetic to our soul and spirit, we ought to aspire for the ultimate question: where did the physical laws come from? In case a complementary solution to this problem is not procured over the next centuries, all we'd be left is a mere "description" of the world we're living in, obviously, a few notches up from the prior, but nearly identical, elucidation. Just my 2 cents.

p.s
This paper is dated to the 23rd of December, and seems to be a nice idea...

Theoretical physics has arrived to the crucial point at which it should fully reexamine the sense and the interrelations of the three fundamental entities: fields, particles and space-time geometry. String theory offers a way to derive the low-energy phenomenology from the unique physics at Plankian scale. However, it doesn’t claim to find the origin of physical laws, the Code of Universe and is in fact nothing but one more attempt to describe Nature (in a possibly the most effective way) but not at all to understand it.

In the interim, twistor structure arises quite naturally in the so called algebrodynamics of physical fields which has been developed in our works. From general viewpoint, the paradigm of algebrodynamics can be thought of as a revive of Pithagorean or Platonean ideas about “Numbers governing physical laws”. As the only (!) postulate of algebrodynamics one admits the existence of a certain unique and exeptional structure, of purely abstract (algebraic) nature, the internal properties of which completely determine both the geometry of physical space-time and the dynamics of physical fields (the latters being also algebraic in nature)

In result, physical picture of theWorld which arises as a consequence of one only algebraic structure appears as very beatiful and unexpected. As its basic elements it contains the primodial light flow – “pre-Light” – and the relativistic aether formed by the latter, multivalued physical fields and prelightborn matter (consisting of particles-caustics formed by the superposition of individual branches of the unique pre-light congruence in the points of their “focusization”)

As very natural and deep seems to be the arising in theory connection between the existence of universal velocity (velocity of “light”) and of the time flow; connection which permits to understand, in a sense, the origin of the Time itself. Time is nothing but the primodial Light; these two entities are undividible. On the other hand, there is nothing in the World except the preLight Flow which gives rise to all the “dense” Matter in the Universe.

So, it seems that negative tension branes are not exclusive of the cyclic model. For example, the Randall-Sundrum I model (RS1), that was proposed in this paper:
"A large mass hierarchy from a small extra dimension"http://arxiv.org/abs/hep-ph/9905221
is a brane-world model consisting of two 3-branes embedded in a five-dimensional Anti-de Sitter space. Our brane is called the TeV brane, and the other is called the Planck brane. Is postulated that our 3-brane has negative tension
A formula for the tension of a D-brane is given in the first page of this paper
"A note on brane tension and M-theory"http://arxiv.org/abs/hep-th/9607011
so, maybe you just have to plug the variables in the formula, and if the result is negative, then that is a negative tension D-brane